python: Replace dict.has_key with 'key in dict'

Python 3 has removed dict.has_key in favour of 'key in dict'.

Change-Id: I9852a5f57d672bea815308eb647a0ce45624fad5
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15987
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/python/m5/util/multidict.py

@@ -43,7 +43,7 @@ class multidict(object):
         return `dict(self.items())`
 
     def __contains__(self, key):
-        return self.local.has_key(key) or self.parent.has_key(key)
+        return key in self.local or key in self.parent
 
     def __delitem__(self, key):
         try: